1. Field of the Invention
The present invention relates to a ball grid array (BGA) semiconductor package using a flexible circuit board and a method for fabricating the same. More particularly, the present invention relates to a BGA semiconductor package using a flexible circuit board, in which the flexible circuit board is mounted with a metallic carrier frame to obtain a thin package structure and to increase the bonding force between an encapsulate and constituting elements of the package, thereby achieving an improvement in the electrical performance and heat discharge performance of circuit patterns, removing a bending phenomenon of the package, and achieving an improvement in the reliability of the package. The present invention also relates to a method for fabricating such a BGA semiconductor package.
2. Description of the Prior Art
Generally, semiconductor packages are adapted to encapsulate a semiconductor chip, which consists of various electronic circuits and wirings bonded thereto in the form of a single device or integrated circuit, using an encapsulant, thereby protecting the semiconductor chip from external environments such as dust, moisture, and electrical and mechanical load. In order to optimize and maximize the performance of the semiconductor chip, such semiconductor packages have a lead frame or printed circuit board (PCB) which provides signal input/output terminals coupled to a main board.
Such semiconductor packages include resin encapsulated packages, tape carrier packages (TCP's), glass encapsulated packages, and metal encapsulated packages. These semiconductor packages are classified into those of the through-hole type and those of the surface mount type. The through-hole type semiconductor packages include dual in-line packages (DIP's) and pin grid array (PGA) packages whereas the surface mount type packages include quad flat packages (QFP's), ball grid array (BGA) packages, and bottom leaded packages (BLP's).
The recent tendency of electronic devices to obtain a compact structure results in a requirement for providing semiconductor packages capable of achieving an increase in the mount density of a main board used. In this regard, BGA semiconductor packages have been mainly used, as compared to DIP's. In particular, BGA semiconductor packages using solder balls as input/output terminals have been mainly used. An example of such BGA semiconductor packages is illustrated in FIG. 1.
As shown in FIG. 1, the BGA semiconductor package, which is denoted by the reference numeral 10', includes a PCB 20'. This PCB 20' has a substrate 25' made of a glass fiber reinforced thermosetting composite. A pair of complex and fine circuit patterns 21' are formed on the upper and lower surfaces of the substrate 25', respectively. The circuit patterns 21' are comprised of conductive plated films formed on the upper and lower surfaces of the substrate 25'. A pair of thin film solder masks 23' made of polymer resin are formed over the circuit patterns 21', respectively. A semiconductor chip 11' is centrally bonded to the upper surface of the PCB 20'. The semiconductor chip 11' has input/output pads 12' bonded to the circuit patterns 21' by means of conductive wires 13'. The upper and lower circuit patterns 21' are connected to each other by means of conductive via holes 24'. A plurality of solder ball lands 22' are formed on the lower circuit pattern 21'. A plurality of solder balls 30', which serve as input/output terminals with respect to a main board, are fused on the solder ball lands 22', respectively. The BGA semiconductor package 20' also includes an encapsulant 14' which is formed to have a one side molded structure using a glob top or epoxy molding compound, thereby protecting the semiconductor chip 11', conductive wires 13' and circuit patterns 21' from the environment.
In the BGA semiconductor package having the above-mentioned configuration, the semiconductor chip 11' has a signal conduction relation with the main board (not shown) via the conductive wires 13', upper circuit pattern 21' of PCB 20', conductive via holes 24', lower circuit pattern 21' of PCB 20', solder ball lands 22' and solder balls 30'. Thus, an electrical function of the semiconductor chip 11' is achieved.
The BGA semiconductor package can easily accommodate a semiconductor chip having a plurality of input/output pads because it has, at the lower surface thereof, a plurality of solder balls serving as input/output terminals. The BGA semiconductor package also has a compact and thin structure. Accordingly, such a BGA semiconductor package has been widely used in various advanced technical fields using semiconductor chips.
However, such a conventional BGA semiconductor package has a problem in that it is difficult to easily discharge heat generated during the operation of the semiconductor chip because the BGA semiconductor package uses a PCB having a large thickness of at least several hundred microns, thereby exhibiting a high thermal resistivity. Furthermore, there is no appropriate heat discharge means in the BGA semiconductor package. As a result, it is difficult to appropriately discharge heat from the semiconductor chip, thereby causing the semiconductor chip and package to crack. A degradation in the electrical performance of the semiconductor chip also occurs.
The thickness of the PCB also results in a difficulty to provide a thin and light package structure. Moreover, the conventional BGA semiconductor package uses elongated signal lines extending from the semiconductor chip to the main board because the input/output pads of the semiconductor chip are electrically connected to an elongated and fine circuit pattern formed on the upper surface of the thermosetting composite substrate of the PCB by conductive wires while the circuit pattern is electrically connected to the main board through conductive via holes, circuit pattern formed on the lower surface of the substrate, solder ball lands and solder balls. The increased length of the signal lines results in an increase in the inductance and impedance in the signal lines. Furthermore, a coupling effect occurs between adjacent circuit patterns, thereby greatly degrading the electrical performance of the semiconductor chip.
Meanwhile, the PCB is easily bent under the condition in which high temperature heat is generated because it has flexibility. When the PCB is bent, the solder balls arranged on the lower surface of the PCB may separate from the main board, thereby causing the semiconductor chip to fail its electrical performance.
Although the electrical performance of semiconductor chips is advanced by virtue of the developments of semiconductor chip design techniques, it is adversely affected by the above-mentioned degraded package structure. Consequently, the conventional package structure is problematic in that it serves as a factor of degrading the electrical performance of semiconductor chips.